Guided-Wave Spatial Combiners

Transcription

1 IMS Workshop June 2 Guided-Wave Spatial Combiners Bob York University of California, Santa Barbara

2 Outline Spatial Power Combining Waveguide-based Combiners X-band Array Development (MAFET) K-band and Coaxial Systems Projections and Summary

3 K-band SSPA Benchmark Data Source: Mike Delaney, Hughes Space & Communications, El Segundo, CA 7 18 GHz Power Devices: Industry Comparison % n cy, ie E fic d d e A e r P o w Industry Trend HRL K4 (Amplifier) HRL K4 (Load Pull) HRL K3 TRW TI Martin marietta Avantek MIT Output Power, Watts

4 Path to Broadband Power ARO MURI High efficiency favors small-area devices Heat removal (see empirical chart) Broad bandwidth favors small-area devices Small Cgs and high output impedance Lower phase noise favors large number of devices Excess phase noise goes as 1/N Conclusion: Use a large number of small devices for broadband power Efficient broadband combining of many devices favors spatial combining

5 Spatial vs. Corporate ARO MURI When does it make sense to use a spatial combiner? Combining efficiency: Binary Wilkinson tree, η =L k, where L=loss per stage, k=number of stages 5 Using general expression for system PAE shown earlier: Assumes: G=1, η a = 5% Spatial combiner: η =L (independent of number of amplifiers) Typical numbers at X-band: Corporate:.15 db loss/stage Spatial:.5dB output loss Transition point: N 16 Power Added Efficiency, % L =.1dB (Corporate) L =.2dB (Corporate) L =.3dB (Corporate) L =.5dB (Spatial) L = 1.dB (Spatial) L = 1.5dB (Spatial) Number of Amplifiers

6 Array Architectures in Spatial Power Combining ARO MURI Tile Approach normal incident/outgoing waves limited bandwidth in general challenge in thermal management Tray Approach parallel incident/outgoing waves broadband characteristics good heat-sinking property

7 Guided-Wave Spatial Combiner Rectangular waveguide MMIC amplifiers Rectangular waveguide Output wave Input wave Microstrip!! Broadband antenna arrays Waveguide environment Input wave! Slotline-to-microstrip transition! Off-the-shelf MMIC amplifiers! Hybrid circuit configuration! Ceramic substrate with good thermal conductivity Tapered-slot transition US Patent: 5,736,98 Awarded April 7, 1998 (University of California)

8 Circuit Topology Modular Tray Architecture Excellent Thermal Property High Power Performance Broadband Characteristics Ease of Operation & Maintenance MMICs Directly Attached to Test Fixture Capability for Large Scale Integration Adapt to Different Device Technology MMIC Amplifier Tapered-Slot Antenna Microstrip Transformer

9 Loss, Gain, PAE P ia P i P dca P oa G Single Amplifier Cell P oa Pia ( G 1) P ηa = = P P dca N-way Combiner System dca Splitter P dca Combiner P ia P oa G P o L i L o ia η sys % E, A P d e a liz N or m Po Pi = P dc ( LiGLo 1) Pi = NP η η L sys a o dca ( LiGLo 1) = ηa L ( G 1) for high gain PAE of pre-amplified system can easily approach combining efficiency based on output losses only i L i = L o =-.2 db L i = L o =-.5 db L i = L o =-1. db 65 Combining Efficiency Power Amplifier Gain (linear) Conclusions: Output losses alone determine ultimate performance of a combiner Input losses can be overcome by pre-amplification

10 8-MMIC (4 tray) Combiner Results presented at 1998 IEEE MTT Symposium (Baltimore), N.-S. Cheng and R. A. York, 2 Watt Spatial Power Combiner in Waveguide,!CW Operation (2x4 Array)!Pout, max = 42.9W!Combining Efficiency 7%!Gain = dB Gain Compression Pout, max = 42.9W at 8.7GHz Pout 5 Pin, dbm Gain Variation = 2.4dB Pin Gain Gain, db Frequency, GHz Primary Sponsorship through MAFET

11 TI 983 MMIC Amplifier Output RF Power, W MMIC #1 MMIC #2 MMIC #3 MMIC #4 MMIC #5 MMIC #6 MMIC #7 MMIC # Frequency, GHz 6.5 to 11.5-GHz Frequency Range 5-Watt Output Power at 7V, 6-Watt at 8V 18-dB Typical Small Signal Gain 35% Power Added Efficiency at 7V, 3% PAE at 8 Volt Bias 12-dB Typical Input Return Loss, 9-dB Typical Output Return Loss On-chip Active Bias Circuit Option Simplifies Biasing We wish to acknowledge the generous support of TriQuint/TI in providing a large quantity of these excellent devices at a substantial discount to the University and MAFET project

12 4W X-band X Array Data Results using 8 MMIC (4-tray) Array Configuration! Return Loss < -1dB! Psat = 43.1W at 8.7GHz! Linear Gain = 18.2dB! Graceful Degradation Return Loss, db Return Loss Measurement Frequency, GHz Gain, linear = 18.2dB Psat = 43.1W Pout, dbm Pout vs. Pin Measurement Pin, dbm Gain, db Pout, dbm MMICs -- 7 MMICs -- 6 MMICs Graceful Degradation Frequency, GHz Gain, db

13 Design of Finline Arrays! Target slotline gaps are specified at both ends! Operating band is specified! Taper length and shape optimized to minimize return loss over the band taper length, L Layout of a single antenna card gap size chosen to match waveguide opening ß Z and b Taper Shape To Be Determined MMIC amplifiers gap size chosen to preset value ß Z L and b Complication: L wave impedances and propagation constants are all functions of frequency. Standard taper theory is based on TEM guides.

14 Computational Results! 2x2 finline array in standard WR-9 waveguide! Propagation constant (effective permittivity) calculated for expected slot widths and frequencies using SDM! Optimized taper designed for S 11 < -2dB from 8-12 GHz y b g 12 GHz 7 GHz c a x no rmalized gap width optimized taper Normalized Slot Width, 2g/b Position along taper, cm Theory assumes taper is matched Need to know target slot-line characteristic impedance

15 Passive Return Loss Measurement Simulation vs. Measurement -5 Two Card Array, optimized taper 1mil AlN substrate 4mm card spacing! Theoretical and measured results agree quite well! Suggests additional impedance transformation needed for 5W MMIC amplifiers Reflection coefficient, db Measured (1 Ohm termination) Theory Frequency, GHz Slotline Antenna with Microstrip Taper -5! Microstrip transformer terminated with 5W chip resistor! Return loss <-15dB for X-band for 2-card system Return Loss, db Frequency, GHz

16 Thermal Simulations Results from Tanner Thermal Simulator Copper carrier, 24 elements (12 W) Four (4) 5-Watt MMICs per tray More cards in standard aperture thinner cards Copper fixture doubles thermal capacity Air-cooled heatsink system will be employed

17 UCSB/HRL 12W System Preliminary Results using 24 MMIC (6-tray) Array Configuration 6 5! CW Operation (6x4 Array)! 4 MMICs on each tray! Pout, max = 126W at 8.1GHz! Gain = dB (8-11GHz)! Vd = 8. V, Pin = 38dBm 6 5 Tapered-Slot Antennas Biasing Pins MMIC Amplifiers Microstrip Transformers Gain, db Pout, dbm Frequency, GHz

18 Overview of Combiner Circuit

19 Graceful Degradation 5 m B d w e r, P o t O utpu P m 2 (1 ) N Number of Device Failures D.B. Rutledge, N.-S. Cheng, R.A. York, R.M. Weikle, and M.P. Delisio, Failures in powercombining arrays, to appear in IEEE Trans. Microwave Theory Tech., 1999

20 15W Combiner (8x4) Preliminary Results using 32 MMIC (8-tray) Array Configuration! CW Operation (8x4 Array)! 4 MMICs on each tray! Pout, max = 15W at 8.1GHz! Gain = dB (8-11GHz)! Vd = 8. V, Pin = 4dBm Tapered-Slot Antennas MMIC Amplifiers 6 Pout, max = 15 Watts at 8.1 GHz 5 Biasing Pins Microstrip Transformers 5 4 Pout, dbm 4 3 Pout Gain = 1. +/- 1.9 db Gain 3 2 Gain, db Combiner DC Bias Frequency, GHz WG Taper Transition

21 K-Band System Oversized WG ARO MURI WR42 waveguide opening Waveguide Opening designed to accommodate the six cards antenna array Horn Antenna Incident Wave The waveguide opening has the dimension of 2.cmX.71cm, which is designed to have at most two modes propagating in the system.

22 2GHz Flip-Chip Amplifier and Tray ARO MURI S21(dB) tray system with 8% C.E. currently under testing -3 S11 MAG [db] S21 MAG [db] S22 MAG [db] Biasing Pad Thin-film Capacitor Frequency [Hz] Input Bonding pad Resistor output Spiral Inductor Bridge All are built monolithically 8.6 mm Design Layout 4 mm

23 Coaxial Combiner System ARO MURI 32 cards 6.67'' o 3 Center Section 1.77''.4 '' 1.2 '' Center Coaxial Section Loaded with Tapered Slotline Cards Inner Conductor Diameter.92 '' Outer Conductor Diameter.21 ''! Antennas uniformly loading an oversized coaxial (TEM) waveguide! Array is uniformly illuminated! No low-frequency cutoff: bandwidth limited by finline transitions! Accomodates large numbers of amplifiers! Electrically and thermally symmetrical Type N (DC-18 GHz) Connector Outer Conductor Inner Conductor

24 5-15 GHz Coaxial Array ARO MURI 32 Card System, 2 transitions per card (64-way splitter/combiner) Broadband coaxial tapers cover 2-2GHz AlN-based slot tapers cover 5-18GHz range Front view of loaded section Exploded perspective

25 32 Card (64-Way) Response ARO MURI Insertion and Return Loss Close-up of insertion loss B -5 B -1-2 w er,d po e v t R el a i cards o -25 S11 S Frequency, GHz w er,d po e v t R el a i -3-4 S21-5 Losses S 2 + S Coax losses -6-7 finline transition cutoff Frequency, GHz 64-way splitter/combiner system 1-2 db insertion loss over 5-2GHz range some suppression of high-order modes Need to improve impedance match cards introduce <1dB loss

26 Conclusions ARO MURI Waveguide Combiners demonstrated Good Combining Efficiency (>7%) C.E. independent of number of devices K-band and Coaxial Systems udner development Some Fundamental issues being explored Influence of non-uniform field Efficiency considerations Improved design concepts Noise & Linearity characterization underway Oversized waveguide environment